The present invention relates to a telescopic tube, comprising a plurality of tube members which are telescopically sliding within each other and whose conical faces are wedged against each other, so that the tube members cannot disengage from each other.
The invention also relates to a continuous method of manufacturing such telescopic tubes from reinforced plastic by successively arranging cores whose length equals that of the tube members and by covering such cores with layers of resin-moistened reinforcing fibers, first a layer of longitudinal fibers which is then covered with a layer of cross-fibers.
The invention relates to the type of telescopic tubes that can be used e.g. as antennae, fishing poles, lampposts, flagpoles etc. The usefulness of telescopic tubes is based on their capability of being retracted to a fraction of their full length for transport and storage.
Traditionally such telescopic tubes are made of tube members which are conical along their entire length. However, a telescopic tube assembly composed of conical tube members has several drawbacks. In order to keep the change of diameter per length unit within reasonable limits, the coning angle must be very small. When the tube members are wedging against each other, this small coning angle produces a great radial force which often damages the ends of the tube members. On the other hand, due to small coning angle, the tube members might be wedged so tightly against each other that retraction of a telescopic tube is not managed by regular force or without damaging the components. When a tube is conical over its entire length, a change of diameter along the entire length will be excessive; thus, the tube is too thick at the base and too thin at the top. This increases the weight of a tube especially when sufficient wall thickness is desired to eliminate the above-mentioned risk of damage.
The manufacture of tube products from reinforced plastic has grown vigorously. However, an automatic machine which produces all-conical telescopic tube will be expensive. This is because the manufacture of long, conical cores is difficult and thus expensive. In a continuously operated manufacturing process, the number of such cores must be up to 50-100. Therefore, the manufacture of conical telescopic tubes from reinforced plastic is not economically profitable by the present technology.
An object of the invention is to provide a novel type of telescopic tube in which the above drawbacks are eliminated and which can be manufactured by a continuous process more economically than heretofore.